Use of bispecific antibodies (bsAbs) to redirect effector T cells for the targeted killing of tumor cells has shown considerable promise both pre-clinically and clinically (see, e.g., Topp et al., 2012, Blood 120:5185-87; Bargou et al., 2008, Science 321:974-77). The bispecific antibodies contain a first binding site specific to CD3 for T-cell recruitment and activation and a second binding site for a targeted disease-associated antigen, such as CD19 (Bassan, 2012, Blood 120:5094-95). The bispecific antibody brings CD3+ T cells into direct contact with targeted disease cells and induces cell-mediated cytotoxicity (Bassan, 2012). Anti-CD3×anti-CD19 bispecific antibodies have been reported to produce a complete and durable molecular remission at very low concentrations in approximately 70% of adult patients with MRD+ ALL (Topp et al., 2012, Blood 120:5185-87). Bispecific antibodies recognizing gliomas and the CD3 epitope on T cells have been successfully used in treating brain tumors in human patients (Nitta, et al. Lancet 1990; 355:368-371).
Numerous methods to produce bispecific antibodies are known (see, e.g. U.S. Pat. No. 7,405,320). Bispecific antibodies can be produced by the quadroma method, which involves the fusion of two different hybridomas, each producing a monoclonal antibody recognizing a different antigenic site (Milstein and Cuello, Nature 1983; 305:537-540). The fused hybridomas are capable of synthesizing two different heavy chains and two different light chains, which can associate randomly to give a heterogeneous population of 10 different antibody structures of which only one of them, amounting to ⅛ of the total antibody molecules, will be bispecific, and therefore must be further purified from the other forms. Fused hybridomas are often less stable cytogenetically than the parent hybridomas, making the generation of a production cell line more problematic.
Another method for producing bispecific antibodies uses heterobifunctional cross-linkers to chemically tether two different monoclonal antibodies, so that the resulting hybrid conjugate will bind to two different targets (Staerz, et al. Nature 1985; 314:628-631; Perez, et al. Nature 1985; 316:354-356). Bispecific antibodies generated by this approach are essentially heteroconjugates of two IgG molecules, which diffuse slowly into tissues and are rapidly removed from the circulation. Bispecific antibodies can also be produced by reduction of each of two parental monoclonal antibodies to the respective half molecules, which are then mixed and allowed to reoxidize to obtain the hybrid structure (Staerz and Bevan. Proc Natl Acad Sci USA 1986; 83:1453-1457). An alternative approach involves chemically cross-linking two or three separately purified Fab′ fragments using appropriate linkers. All these chemical methods are undesirable for commercial development due to high manufacturing cost, laborious production process, extensive purification steps, low yields (<20%), and heterogeneous products.
Discrete VH and VL domains of antibodies produced by recombinant DNA technology may pair with each other to form a dimer (recombinant Fv fragment) with binding capability (U.S. Pat. No. 4,642,334). However, such non-covalently associated molecules are not sufficiently stable under physiological conditions to have any practical use. Cognate VH and VL domains can be joined with a peptide linker of appropriate composition and length (usually consisting of more than 12 amino acid residues) to form a single-chain Fv (scFv) with binding activity. Methods of manufacturing scFv-based agents of multivalency and multispecificity by varying the linker length were disclosed in U.S. Pat. No. 5,844,094, U.S. Pat. No. 5,837,242 and WO 98/44001. Common problems that have been frequently associated with generating scFv-based agents of multivalency and multispecificity are low expression levels, heterogeneous products, instability in solution leading to aggregates, instability in serum, and impaired affinity.
Several bispecific antibodies targeting CD3 and CD19 are in clinical development. An scFv-based bispecific antibody construct, known as BITE® (Bispecific T-cell Engager) employs a single polypeptide containing 2 antigen-binding specificities, each contributed by a cognate VH and VL, linked in tandem via a flexible linker (see, e.g., Nagorsen et al., 2009, Leukemia & Lymphoma 50:886-91; Amann et al., 2009, J Immunother 32:453-64; Baeuerle and Reinhardt, 2009, Cancer Res 69:4941-44). Another bispecific antibody called DART® (Dual-Affinity Re-Targeting) utilizes a disulfide-stabilized diabody design (see, e.g., Moore et al., 2011, Blood 117:4542-51; Veri et al., 2010, Arthritis Rheum 62:1933-43). Both BITE® and DART® exhibit fast blood clearance due to their small size (˜55 kDa), which requires frequent administration to maintain therapeutic levels of the bispecific antibodies.
A need exists for methods and compositions to generate improved bispecific antibody complexes with longer T1/2, better pharmacokinetic properties, increased in vivo stability and/or improved in vivo efficacy. A further need exists for compositions and methods to improve the efficacy of anti-CD3 based bispecific antibodies for therapeutic use in cancer and other diseases, for example by co-administering adjunct therapeutic agents, such as interferons, that enhance the efficacy of the bispecific antibody constructs.